1. Field of the Invention
The present invention relates to a lock device for seatback which can hold a seatback of a vehicle seat at a predetermined angle, and which can self-lock upon upward pivoting of the seatback.
2. Description of the Prior Art
Hitherto, various types of lock devices for automotive pivotal seatback have been developed, one of which is described in Japanese Utility Model Second Publication 7-10946.
The lock device of the publication generally comprises a lock pin provided in the seatback, a spring for biasing the lock pin toward a lock position and a lock plate fixed to a side wall of a vehicle. That is, when the seatback comes to a desired angular position relative to a seat cushion, the lock pin is engaged with a lock hole of the lock plate due to the force of the spring. Upon this, the seatback is locked at the desired angular position. The lock device further comprises a self-lock mechanism by which self-locking of the lock device is carried out upon pivoting of the seatback from a forward folded position to a raised position. The self-lock mechanism comprises a guided pin fixed to the lock pin and a guide portion provided by the lock plate. Upon the upward pivoting of the seatback, the guided pin rises up and slides on the guide portion until the lock pin arrives at a position at which it engages with the lock hole. That is, until arrival of the lock pin at the position, the guided pin holds the lock pin at an unlocking position against the force of the spring, and thus upon arrival, the lock pin is moved until it engages the lock hole, enabling self-locking of the lock device.
However, since the guide portion provided by the lock plate is exposed to the vehicle compartment, the conventional lock device has an unsatisfactory external view. Furthermore, noise is produced by the sliding of the guided pin in the guide portion because the sliding is done against the force of the spring. Furthermore, when forward pivoting of the seatback is needed, the lock pin must be lifted high enough to avoid collision with the guide portion that tends to occur during the forward pivoting of the seatback. Thus, a large manipulated variable of the lock pin is needed, which causes poor operability of the lock device.